Inheriting both haploid chromosome sets from a single parent leads to abnormal peri-implantation mammalian development. This phenomenon occurs spontaneously as a result of parthenogenetic activation, leading to ovarian cystic teratomas in women, or can occur if the egg is fertilized by two sperm, leading to hydatidiform mole during pregnancy. The aberrant development of such isoparental embryos can be studied in mice, where parthenogenetic or androgenetic development can be experimentally induced. The developmental consequences of parthenogenesis in mice are more severe for the extraembryonic lineages than for the embryo proper; the consequences of androgenesis are the opposite, being more severe for the embryonic lineages than for the trophoblast. This pattern of developmental failure has led to the conclusion that the chromosomes are imprinted during gametogenesis in a way that influences their function. Moreover, imprinting results in complementary genetic roles for the egg and sperm chromosome sets, so that they must be located in the same cell for normal peri-implantation development to occur. The central hypothesis of this project is that imprinting causes differential expression of maternal and paternal alleles of specific genes, resulting in abnormal development. The purpose of the project is to determine the identity of these genes. This will be accomplished by examining in detail how imprinting affects parthenogenetic and androgenetic development. The first Aim is to determine the morphology and cell population dynamics of parthenogenotes and androgenotes, in comparison with normal embryos, using light and electron microscopic methods, plus microinjection of lineage tracers to study individual cells. The second Aim is to determine whether isoparental embryos differ from normal in the pattern of tissue-specific gene expression using computerized two dimensional gel analysis. The third Aim is to determine whether genes involved in cell proliferation and interaction are expressed aberrantly in isoparental embryos using a modification of the polymerase chain reaction and in situ hybridization to assay mRNAs for specific growth factor receptors and proto-oncogenes and for cell-extracellular matrix receptors, the integrins. The fourth Aim is to examine the nature of the imprint itself by studying DNA methylation in endogenous genes of isoparental embryos and in transgenes. The results of these studies should provide insight into human ovarian and trophoblastic disease, as well as early pregnancy wastage and infertility.